In my db directory, I can see files called je.info.0 and je.info.0.lck but they are 0 bytes long.
Any pointers as to what may be going wrong? Here is the log:

SEVERE: Allocate exception for servlet search
java.io.IOException: Couldn't get lock for /media/ephemeral0/wikipedia-miner-1.2.0/db/je.info
at java.util.logging.FileHandler.openFiles(FileHandler.java:389)
at java.util.logging.FileHandler.<init>(FileHandler.java:363)
at com.sleepycat.je.util.FileHandler.<init>(FileHandler.java:54)
at com.sleepycat.je.dbi.EnvironmentImpl.initFileHandler(EnvironmentImpl.java:1323)
at com.sleepycat.je.dbi.EnvironmentImpl.<init>(EnvironmentImpl.java:429)
at com.sleepycat.je.dbi.EnvironmentImpl.<init>(EnvironmentImpl.java:341)
at com.sleepycat.je.dbi.DbEnvPool.getEnvironment(DbEnvPool.java:181)
at com.sleepycat.je.Environment.makeEnvironmentImpl(Environment.java:229)
at com.sleepycat.je.Environment.<init>(Environment.java:211)
at com.sleepycat.je.Environment.<init>(Environment.java:165)
at org.wikipedia.miner.db.WEnvironment.<init>(Unknown Source)
at org.wikipedia.miner.model.Wikipedia.<init>(Unknown Source)
at org.wikipedia.miner.service.ServiceHub.<init>(Unknown Source)
at org.wikipedia.miner.service.ServiceHub.getInstance(Unknown Source)
at org.wikipedia.miner.service.Service.init(Unknown Source)
at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1266)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1185)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:857)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:136)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)

Thanks for you input ejmeij.
The service didn't have permission to create the file in the db directory. Once I changed the permissions, it got fixed.

BTW, if you have hosted this service yourself, could you tell me how to change the responseFormat parameter to json? It works directly on the original service by just adding &responseFormat=json but when I try this on the service I hosted, it still gives me an xml output.